R help - Feb 2004 - xypplot (lattice): colours of lines

Using data from a multicenter study with a parallel-group design comparing
two treatments, I plotted each subject's time change of X after stratifying
for center:

xyplot(X ~ time | center, type="l", panel=panel.superpose,
groups=subject)

Now I want these lines to take different colours according to the variable
"treatment". Any help?
Umberto

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On Wednesday 04 February 2004 04:03, Umberto Maggiore
wrote:
> Using data from a multicenter study with a parallel-group design comparing
> two treatments, I plotted each subject's time change of X after
stratifying
> for center:
>
> xyplot(X ~ time | center, type="l", panel=panel.superpose,
groups=subject)
>
> Now I want these lines to take different colours according to the variable
> "treatment". Any help?
Umm, you should already have lines colored differently by different 
'subject's. Do you want to further differentiate by treatment ? 

If that's so, there's probably no good way. You could try creating a new
factor combining subject and treatment and use that as the groups argument, 
e.g.,

factor(paste(as.character(subject), as.character(treatment), sep =
"/"))

Deepayan